3.7 merc. low oil pressure

[ericcarr2000]

Ok heres what I have going on now. I just got done dropping her in the water for the first time of the year. When it was in the driveway hooked up on muffs, I didn't notice the problem. After I got it out and opened it up I noticed the oil pressure was ok at 40 P.S.I. I backed off the throttle and there the pressure went all the way down to about 8 or 10 P.S.I......The motor is a 3.7 mercruiser motor that was blueprinted and has only 101 hours on her. What could be causing the low oil pressure? In order to get the pressure up to about 35-40 P.S.I. I need to throttle it to about 3500 R.P.M.'s...:faint2:

 

[NHGuy]

Re: 3.7 merc. low oil pressure

How is the oil level? How old is the oil and what viscosity did you use? Was the motor super hot? Does it have more pressure when the oil is cold?
If you need to verify psi get a manual pressure gauge and check it against the electric one. That's the quickest and cheapest way to see if the gauge is right or wrong.

 

[ericcarr2000]

Re: 3.7 merc. low oil pressure

I just got done changing the oil over to the 25 W 40 oil. The motor didn't get hot at all and yes it has better pressure when the oil is cold.

 

[ericcarr2000]

Re: 3.7 merc. low oil pressure

You know what, I just thought about this. Last season I ran 10 W 30 oil in her and didn't have not one single problem pertaining to the oil pressure. I was told that according to the manual I need to be running 25 W 40 oil so I changed the oil from the 10W30 from last season over to the 25W40 and that seems to be where the problems begin. As I stated before while I had the motor running in the driveway, it never really didn't get up to temperature, the pressure was fine at around 40 P.S.I. at idle. Today I noticed that after I had her out in the water and was able to open her up and get her up to temperature that's when the P.S.I.'s dropped, while at around 1000 R.P.M.'s to idle. Should I try to go back to the 10W30 oil where I knew I has good pressure or should I do as the manual states and run the 25W40? It just seems funny that the 25W40 oil, which correct me if im wrong, is thicker than the 10W30 oil and would have that huge affect on oil pressure while warmed up....Give me your thoughts on this one...

 

[generator12]

Re: 3.7 merc. low oil pressure

If you're seeing an honest 10 PSI at idle speed, you're in a lot of good company. 40 PSI at 3000 RPM might actually be a little low - not necessarily a problem, but lower than I'd expect to see.

NH had a point when he told you to double check the pressure with a known good gauge before working yourself into a sweat over this. If it indicates that your readings are correct, going to a lower viscosity won't increase your oil pressure.

 

[nola mike]

Re: 3.7 merc. low oil pressure

Minimum is 15 psi @ 2k rpm. Dude, you need to get out and enjoy your boat...you'll have plenty of stuff to fix on that 470without having to go looking for it

 

[Levinz11]

Re: 3.7 merc. low oil pressure

I've always believed that 10 PSI per 1000 RPM's is fine. I have an old S-10 that hovers at 10 PSI at idle and about 40 PSI when on the freeway (2.2L).

 

[ericcarr2000]

Re: 3.7 merc. low oil pressure

LOL, I know that Mike and found that out the hard way trust me... that's why im going to be selling it after this seasons over with and try to get in a bigger boat. It just seems my pressure was much better last year running the stinking 10W30 is all...:happy:

Minimum is 15 psi @ 2k rpm. Dude, you need to get out and enjoy your boat...you'll have plenty of stuff to fix on that 470without having to go looking for it

 

[stonyloam]

Re: 3.7 merc. low oil pressure

25W40 should give you higher pressure than 10W30 because it has a higher viscosity at all temperatures.

 

[ericcarr2000]

Re: 3.7 merc. low oil pressure

Ok, I know this might sound like a stupid question but is there any way that that stinking oil pressure sending unit can be at fault, it was the original one on the old motor and I didn't replace it when I put the new motor in her.....:cold: I WILL be installing a mechanical oil pressure gauge in place of that sending unit just to check to see if it at fault.

 

[stonyloam]

Re: 3.7 merc. low oil pressure

You are obsessing here. if you have more than 15 psi at 2000 RPM you are OK! Listen to nola mike, don't worry, just enjoy

 

[ericcarr2000]

Re: 3.7 merc. low oil pressure

Ok, heres the latest. Just got back from sitting in the boat at the dock, afraid to take her out that far with this oil pressure problem...I checked the dipstick and noticed that the oil level was quite low, about 2 quarts or so.....SO I know my pressure problem was due to low oil....I looked around to see if I could see on the outside if there were any oil leaks, and could not.....I will look again sometime this next week though so I can see better in the day time instead of the nighttime...I can only hope that I can pinpoint the leak quickly.....As I stated before the thing only has 101 hours on it so there cant be any major internal problems with it, at least I hope not....
Stay tuned....

 

[ericcarr2000]

Re: 3.7 merc. low oil pressure

Ok....I finally come to the conclusion that I must be paranoid or something because I took her out for the day...ALL day....and when I first started her up the pressure was real good at about 55 pounds....after awhile I noticed that once it was warmed up the pressure did seem to drop a bit......once I put her in neutral, my pressure was around 15-20 pounds. I must have thought that last year was better for some reason. I am used to an automobile motor instead of these marine machines I guess. After all was said and done, the idle pressure was 15-20 pounds and at W.O.T. the pressure was about 40 pounds. I guess all is good I would assume?
Gary

 

[spdracr39]

Re: 3.7 merc. low oil pressure

Doesn't sound too bad. Where did you decide you missing 2 quarts of oil went?

 

[ericcarr2000]

Re: 3.7 merc. low oil pressure

Well, when I checked it that "night" I assumed the reason I mis-read it was due to it being dark out. Today the first thing I did was check the oil and it was perfect, so I started her up and went on my way monitoring the oil pressure closely. I just don't like the fact that the pressure is as low as it is when its idling at temperature is all...

Doesn't sound too bad. Where did you decide you missing 2 quarts of oil went?